IS-GPS-200H (797934), страница 31
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EachNMCT contains a two-bit availability indicator (AI) followed by 30 slots which may contain upto 30 valid six-bit ERD values. The layout of these 31 data items is as shown in Figure 40-1.The two-bit AI in bits 9 and 10 of word three of page 13 of subframe 4 provide the user with thefollowing information.AI Navigation Message Correction Table Availability00 The correction table is unencrypted and is available to both precise positioning serviceusers and standard positioning service users.01 The correction table is encrypted and is available only tousers (normal mode).precise positioning service10 No correction table available for either precise positioning service users or standardpositioning service users.11 Reserved.212IS-GPS-200H24 Sep 2013Each one of the 30 six-bit ERD slots in bits 11 through 24 of word three, bits 1 through 24 ofwords four through nine, and bits 1 through 22 of word ten of page 13 of subframe 4 willcorrespond to an ERD value for a particular SV ID.
There are 31 possible SV IDs that theseERD slots may correspond to, ranging from SV ID 65 to SV ID 95. The correspondencebetween the 30 ERD slots and the 31 possible SV IDs depends on the SV ID of the particulartransmitting SV in accordance with the following two rules: 1) the CS shall ensure via uploadthat no SV shall transmit an NMCT containing an ERD value which applies to its own SV ID,and 2) the CS shall ensure via upload that all ERD values shall be transmitted in ascendingnumerical slot order of the corresponding SV ID.
To illustrate: the SV operating as SV ID 65will transmit (in order) ERD values which correspond to SV ID 66 through SV ID 95 in ERDslots 1 through 30 respectively, while the SV operating as SV ID 95 will transmit ERD valueswhich correspond to SV ID 65 through SV ID 94 in ERD slots 1 through 30 respectively.Each ERD value contained in an NMCT ERD slot shall be represented as a six-bit two’scomplement field with the sign bit occupying the MSB and an LSB of 0.3 meters for an effectiverange of ±9.3 m. A binary value of “100000” shall indicate that no valid ERD for thecorresponding SV ID is present in that slot.40.3.3.5.2 Algorithms Related to Subframe 4 and 5 Data.The algorithms related to subframe 4 and 5 data shall be as specified in Appendix II, Section20.3.3.5.2.40.3.4 Timing Relationships.The timing relationships shall be as specified in Appendix II, Section 20.3.4.40.3.5 Data Frame Parity.The data frame parity shall be as specified in Appendix II, Section 20.3.5.213IS-GPS-200H24 Sep 2013.
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